This section illustrates useful background information without admission of any technique described herein representative of the state of the art.
Various metering devices such as pulse sensors have become more common for people to measure their own heart rate, movements or other parameters. A new term quantified self has appeared for the desire to quantify all possible parameters that effect on the physical health of oneself. Metering devices help people measuring themselves for such a purpose, but people who want to measure the effects and control their physical exercise based on pulse, for example.
Pulse measurement is typically performed using a chest strap that is worn under clothes and maintains electric cardiac sensors sensor in place on the skin of the user so that heart beat can be computed from the signals produced by the sensor. The strap is yet awkward to wear and there are companies that have launched or are about to launch wrist worn watch-like pulse sensors, often combined with accelerometers for acting as pedometer.
Some measurements such as optical heart rate measurement require that the sensor is either located at a particular location to which skin access is not convenient to provide in the middle of a day or that the sensor is kept very stably on skin. For the latter need, a device is known that biases a sensor against skin with a spring so as to compensate for shake that would easily otherwise break the contact and prevent reliable measurement.